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Bio IB > 2.7a & 7.1b DNA replication > Flashcards

2.7a & 7.1b DNA replication Flashcards

1
Q

Distinguish between a nucleotide and a nucleic acid.

A

Nucleotide is a monomer for nucleic acid

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2
Q

What are the parts that make up a nucleotide

A

Phosphate
nitrogen base
Deoxyribose sugar

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3
Q

What are the complementary base pairs for DNA?

A

Thymine - Adenine
Cytosin - Guarine

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4
Q

What is DNA replication

A

The process where the cell replicates itself in preperation to divide

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5
Q

Which part of the cell cycle does DNA replication occur?

A

Synthesis phase (After G1) (Before G2)

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6
Q

Enzymes involved in DNA replication and their roles

A
  1. Helicase (Unzipping enzyme starting at origin)
  2. DNA Gyrase (Prevents supercoiling back into helix)
    3.** Single Strand Binding proteins - SSBP** (Attach to unzipped DNA bases, preventing hydrogen bonds, hold it open)
    4.DNA Primase (Lays down an RNA primer on complementary base pairs, A-U & C-G)
    5.DNA Polymerase 3 (Builds and adds nucleotides replacing the RNA foundation in 5’ to 3’) (works in leading and lagging strand) (lagging = okazaki fragments, backwards)
    6.DNA Polymerase 1 (removes RNA primers from lagging strand and replaces with DNA nucleotides)
    7.Ligase (glues the nucleotides together with covalent bonds)
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7
Q

Telomeres

A
  • End caps on chromosomes
  • protect DNA by inhibiting DNA replication to the end of chromosomes (prevent DNA being lost during restoration)
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8
Q

DNA sequencing

A

The porocess by which the base order of a nucleotide is elucidated
(Sanger sequencing)

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9
Q

Explain sanger sequencing

8 Mark

A
  1. 4x PCR mixes are set up, each with of normal nucleotides and one dideoxynucleotide (ddA), (ddT), (ddC), (ddG)
    ATCG
  2. Base fragments are separated using gel electrophoresis
  3. The base sequence is determined by ordering okazaki fragments by length
  4. The smaller the molecule, the further it will travel in the gel
  5. Reading from bottom to top of the gel, we can decipher the order of the bases.
  • If ddGTP terminates the sequence after 8 nucleotides, then the 8th nucleotide must be cytosine
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10
Q

Explain DNA replicaiton in prokaryotes

8 mark

A
  1. In prokaryotes, helicase breaks the hydrogen bonds of the complementary base pairs
  2. Gyrase then prevents the DNA strands from supercoiling again and releases tension.
  3. Single stranded binding proteins bind the split strands to prevent hydrogen bonds reforming between complementary bases
  4. A primer then places a peice of RNA on the split adult stand as a foundation for the daughter strand
  5. DNA polymerase 3 then lays down and builds the daughter strand of DNA starting at the origin of the leading strand and multiple origins on the lagginf strand.
  6. The polymerase 3 on the lagging strand works backwards in okazaki fragments in 5’ to 3’.
  7. The Leading strand works smoothly in 5’ to 3’ due to DNA having anti-parallel stands
  8. DNA polymerase 1 then removes the RNA primer replacing it with complementary nucleotide bases.
  9. Ligase then glues the nucleotides together with covalent bonds
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11
Q

Meselson and Stahl

A

Conservative Model – An entirely new molecule is synthesised from a DNA template (which remains unaltered)

Semi-Conservative Model – Each new molecule consists of one newly synthesised strand and one template strand

Dispersive Model – New molecules are made of segments of new and old DNA

  • Proved DNA replication was semi-conservative
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12
Q

Meselson and Stahl Experiment

A

used radioactive isotopes of nitrogen (N14, light & N15, heavy)

Nitrogen is a key component of DNA

  • DNA molecules were prepared using the heavier 15N and then induced to replicate in the presence of the lighter 14N
  • E-Coli grew up in N14 or N15
  • After generations, DNA in E-Coli contained N14 or N15
  • E-coli solutions were mixed and centrifuged
  • N15 was further down due to density
  • N14 and N15 was then mixed for replication
  1. Gen 0, 100% DNA was in heavy form
  2. Gen 1, 100% of DNA intermediate
  3. Gen 2, 50% light & 50% intermediate
  4. This proved semi-conservative replication
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13
Q

Components of a nucleosome

A

DNA tightly wrapped twice around 8 Histones, plus a binder histone

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14
Q

Draw a labelled diagram of a section of DNA showing 4 nucleotides

A

O = phosphate
Hexagon = deoxyribose sugars
/ = covalent bonds

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15
Q

Rosalind Franklin and Maurice Wilkins

A
  • Used a method of X-ray diffraction to investigate the structure of DNA
  • Rosalind discovered the 2 backbones had to run in seperate directions
  • Maurice showed a photo of an X-ray revealing the helix model to Watson and Crick without her permission
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16
Q

Erwin Chargaff

A
  • Discovered that the number of A+T is the same and C+G is the same
  • Watson used this to discover they are paired
17
Q

Linus Pauling

A

Him, Watson and Crick suspected that DNA was helix
- proposed a triple helix
- Led to Cricks discovery of X-ray diffraction pattern of what the helix should look like

18
Q

Watson and crick

A

Used Rosalind Franklins X-Ray photo
- Discovered the structural organisation of the DNA molecule
- By creating a model, they used Linus Paulings findings of the complementary base pairs to see that they matched up.
- With this they built the double helix structure of DNA, rejecting Erwin Chargaff’s tripple helix hypothesis.

19
Q

Hershey and Chase experiment

A
  1. They infected viruses with radioactive S35 (sulfur) and 32P (phosphate) which are both radioactive isotopes of the natural element.
  2. They then got bacteria (e-coli) and infected it to see if the bacteria would absorb the radioactive isotopes.
  3. It was found that the bacteria absorbed the 32P due to having phosphate backbones in DNA and no 35S.
  4. This concluded that DNA is the genetic hereditory material, and not proteins.
20
Q

Introns Vs Exons

A
  • Introns stay inside the nucleous, and are recycled into nucleotides
  • Exons exit tue nucleous and are transcribed in transcription

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